I saw those and was wondering the same thing. I did a little checking and was told that not all guns will except all powders. Being I spoke to someone that does powder coating, I want to believe him but then again, he may have said that cuz it may cut into his biz.
If it's true, then there's a limitation on the kinds and colors. That little gun looked pretty cool though.
If you're looking to get a p/c gun, check out Eastwood (www.eastwood.com), they've got a few guns and lots of colors.